1. Field
Example embodiments relate to photolithography using extreme ultraviolet (EUV) light for semiconductor fabrication. In particular, example embodiments relate to a reflective photomask for monitoring a pattern shift caused by a change in position of the focus of light, methods of fabricating the reflective photomask, a reflective illumination system using the reflective photomask, and a method of using the reflective photomask.
2. Description of the Related Art
In a photolithography technique for semiconductor fabrication the focus of light should be optimally located on a wafer. Therefore, the procedures of measuring a depth of focus (DOF) for forming an image according to a position shift of the focus of light, determining an optimum position of the focus, and controlling a photolithography process based on the optimum position of the focus may significantly improve productivity of semiconductor fabrication technology.
For example, the focus of light may change by replacing any part of an illumination system of the photolithography equipment, thereby requiring frequent monitoring of the change in position of the focus of light. However, a conventional device and method for monitoring a change in position of the focus of light, e.g., a pattern used for monitoring a change in position of the focus of light in a transparent illumination system, cannot be used in a reflective illumination system that uses EUV light.